Synthetic material



Patented Apr. 21 1942 William Hcnry'bfoss, Iiondon, England, assignor v to (leia'nese Corporation of America. a ear-pom tion or Delaware Ne Drawing. Application mm 1a use-serial 531225.570. In Great Britain September 14,

9 Claims. "(L 2-14 j This invention relates to synthetic, materials such as sheets,nlms,foils. coatings and the like having arbasisof cellulose acetate or other organic derivative of cellulose, to compositions suitable for the production of such materials, to

articles embodying such materials and to cellulose derivatives suitable for use in the production of such compositions, materials and articles.

Materials of the kind referred to above when exposed to a moist atmosphere in general become logged in the same way as glass does when an exposed. This is a disadvantage particularly when the materials in question are used for such purposes as the manufacture oi eye pieces in respirators .or goggles or of windows, e. g. in aircraft. I have now iound that by acetylating cellulose and hydrolysing'the resulting primary acetate to a point considerably beyond the inception of acetone solubility, a cellulose acetate can be obtained whlch although insoluble and resistant to liquid water is nevertheless soluble in acetone diluted to a considerable ektent with water and that from such a cellulose acet'aie'.'nln1s, foils,

ta'ric acid' with glycerol, formal glycerol and glycol. The synthetic realm of this kind which are soluble in water orsin' aqueous acetone are particularly suitable.

. The invention includes articles, for example, respirator face-pieces, aircraft and land vehicles and such that whenin use said window is liable to be exposed on one side to a moist warm atmosphere and on the other side to a colder atmosphere, said window having a transparent closure comprising a sheet at least one surface of which is composed largely-of an organic derlva tlve of cellulose having the solubility properties referred toabove. The sheet may be composed largely of the special organic derivative of celluhaving an enclosedspace provided with a window lose throughout: or a composite sheet may be employedpfor example, one formed by sticking a 1 sheet composed largely of. the special organic sheets, coatings and likematerlal can be made which are substantially free frorn 'the disadvantage reierr'edto above. particularly when the materials contain in addition to the cellulose acetate of 'special solubility propertie's a modifier (c.g. a plasticiser or synthetic resinihaving an affinity for water. I have further found that by similar methods, materials havingthe desired P w rtie's'can be made with a'basis of other organic derivatives, particularly organic esters of cellulose.

The sheet materialsoi' the present invention have a basis of an organic derivative oi cellulose which is'insoluble in water butis soluble in a linuid mixture containing a-neutral organic liquid and at least an equal amount oi water, Preferahlir, the materials contain in addition a modifier for thecellul'ose derivative. hi vlng an affinity ior water, i. e. a substance. iors'example, a plastl'ciser orsynthetlc'resin. which inodlfles the physicalpropertics of the shee't material which has an aliinlty for water Amongmodiflers which are derivative of cellulose to a sheet oi glass or other water impermeable] material, the composite sheet being so positioned that'the surface containing the organic derivative of cellulose is the surface 'liahle to-be exposedto the moist warm atmospherein the use of the article; Thus. for exiampie. in a respirator i'ace-piece,:the' eye-piece or ,eyefplecesmaybe composedoi sheets of glass stuckjto sheets of the material-containing the special organic derivative of cellulose and ar-' ranged so that the said material is on'the inside of the lace-piece. An "alternative" andin most cases preferable arrangement is to separate the sheets of glass orqcther. impermeable'material in land vehicles and aircraft.

plasticizers 'fororga'nic derivativesjof cellulose,

mention may'bemade oi diacetin, triaee'tin; di slycerine acetate, dimethyl phthalate and "980itener 90; other plasticisers may be present. for exa ple, dlethyi phthalate, dimethyl. diethyland dlbutyl iartrates. methyl glycol pht aisle and" trichlorbutyl phosphater Among niod are which aresynthetic-resins speclal'mention may be made oi those obtainable by condensing an alcohol containing at least two hydroiry groups with a hydro u polycarbonlic acid, a formal of such an "ioidor a fatty'iacid ester of such an acid. Such ru lns'are described in BritishPatent No. 4535833,

j and condensation products of citric acid,

methylene citric acidfacetyi citric acid and tar- 'and of the cellulose derivative material by an airspace, the sheet ofcellulose derivative material again being onthe inside of the facepiece. From. the point of view of resistance to dimming over a long period. however, a simple sheet of the cellulose derivative material for closing the window aperturels the most satisfactory arrangement, Similar arrangements to those described for res pirator eye-pieces can be adopted in providing windows or windscreens for Compoeitesheet materials may also be closed compartirlhhts sticking the sheet matcrial containing mermai material such as gelatin or coating the cellulose derivativesheet material with acompositlon having 'a' basis-oi such water permeable material.

The sheet materials oi the invention canalso be used for surfacing wood. paper or other opaque organic derivativeofcellulose to water permeable materials although their principal utility 'is in: making transparent window closures, The lnvention includes the production oi the special cellulose derivatives having the solubility propertles specified aboveand also the derivatives themselves and compositions of matterlcontainq ing these derivatives. The celluloseiderlvativel l of the invention are preferably organic esters of,

cellulose.

cellulose. They may be made by ripening an organic ester of cellulose in solution until the desired solubility properties are obtained. The attainment oi these properties by ripening is expedited either by pretreatlng the cellulose from which the ester is to be made, e. g. with iormic acid or acetic acid in admixture with a small proportion of hydrochloric or sulphuric acid. under such conditions as to break down to some extent the cellulose chains; or by conducting esteriflcation or the cellulose under more vigorous conditions than is usual, for example, in the presence or a relatively high amount. e. g. -20% 0! sulphuric acid or like acting esterification catalyst and/or by allowing the temperature to rise considerably during esteriflcation.

The organic derivative 01 cellulose is preferably a cellulose acetate which is soluble in a liquid mixture containing acetone and at least anequal amount of water. The cellulose acetate may be soluble in even more dilute solutions of acetone. for example, solutions containing acetone and water in the proportions of 40 or 45 to 60 or 55. Instead of celullose acetate, other organic esters oi! cellulose may be employed, for example, cellulose propionate or butyrate. The invention moreover includes the production and use of cellulose ethers having the desired solubility prop.- erties, for example, methyl. ethyl and oxyethyl In the production of such others the desired solubility properties can readily be obtained by controlling the degree of maturing oi the alkali cellulose before etheriflcation.

The compositions oi the invention contain the special cellulose derivatives in solution in a liquid mixture containing a volatile neutral organic solvent, at least 30% oi water, a medium or high boiling solvent and/or a modifier having an alflnity for water. Among medium or high boiling solvents or particular value with the cellulose acetates of the invention, mention may be made of ethyl lactate, the monomethyl ether oi. ethylone glycol, diacetone alcohol. cyclohexanone. methyl cyclohexanone and ethyl iso-oxybutyrate. The compositions may contain any oi! the modii'iers having an amnity for water referred to above in connection with the composition of the sheet materials. The presence 0! the medium or high boiling. solvent facilitates the production 01 sheets, nlms, coatings and the like by evaporation oi' the compositions without "blushing? The presence of the modifier having an amnity ior water, and particularly a modifier which is a synthetic resin 0! the class referred to above. in-

. creases the resistance of the sheets, aims and other materials made from the compositions to dimming in the presence of a moist atmosphere. Amos 1 suitable volatile neutral organic solvents ior us in the compositions of the invention are acetone. dloxane, methyl ethyl ketone and methylehe ethylene ether.

The amount of water in the solvent mixtures oi the compositions should be at least 30% and may be considerably higher, e. x, 40-45-5096 or even higher. At least a proportion 01 the acetone or other volatile solvent in the solvent mixture can be replaced by alcohol. so. cheapening the process which is already considerably cheaper than ordinary processes for the manufacture oi films and like materials from cellulose acetate involving the use on substantially anhydrous acetone as the solvent. I have found for example. that with the special cellulose acetates of the invention excellent results are obtainable 25% alcohol; 50% water, or 10% acetone; 60% alcohol: 30% water. a small addition. for example, 4-5 or 6% of ethyl lactate. diacetone alcohol or like medium or high boiling solvent being made in each case;

Apart from the special synthetic resins having an aillnity for water referred to above other synthetic resins may also be present in the compositions ol' the invention. Among such resins, mention may be made of the dlphenylol'propaneacetone and diphenylol-propane-tormaldehyde resins and also of the formaldehyde-toluene-sulphonarnide resins. Such resins are not in general soluble in mixtures containing a large proportion of water for example 50% aqueous acetone. When they are employed, therefore, the solvent mixture should either contain a lower proportion of water and a higher proportion of organic liquids such as alcohol or should be such that on evaporation of the volatile constituents. the mixture of less volatile constituents remaining is capable of dissolving the resins. When such a solvent mixture is used the resins may be initially applied in dispersed form so that on evaporation oi the volatile solvent they dissolve.

Sheet materials oi the kind referred to above can be made by flowing the compositions of the invention on to suitable surfaces and evaporating the solvent and from such materials eye-pieces for respirators or other window closures can be cut or stamped.

As indicated above one of the most important applications oi. the invention is in the production oi transparent sheet material suitable ior the production of respirator eye-pieces or for similar applications where the maintenance of transparency in a moist atmosphere is required. The esters oi. the invention and compositions containing them have, however. .many other applications. Thus. apart from the manufacture of transparent films. foils and sheets such compositions can beused lor coating wood. paper, tabrics or other materials. The cheapness ol the solvent mixture is an important advantage 01 such applications. The compositions and also foils made therefrom can be used as adhesives, for example. in sticking ordinary cellulose acetate material to wood, paper or other materials, particularly cellulosic materials. The in vention also includes the production 01 composite transparent materials made by surfacing a sheet or film of ordinary cellulose acetate or other A film-forming solution of the iollowing constitution is made up as follows:

Parts Special cellulose acetate 20 Water Acetone 40 Methyl cellosolve 60 the parts being by weight. The special cellulose acetate is a cellulose acetate having a maximum solubility in a 50% aqueous solution 0! acetone.

The composition is flowed on to a suitable ill-niorming surface to produce a him about 0.010"

thick. Dises'oi suitable size n. stamped mm except that the fllm lol'mlnl solutlonhas the this film for the production of respirator eye lollowinfl'conipositionz pieces. 'Other compositions'that can be used in Parts the same wayare: Special cellulose aoetaie- 20 5 Methylene citric acld-ylycerol resin 10 .3 2 Dionne 50 t p h Water so S ia cellulose mu 20 Glycerine 1 313 f? methylene glycol 3 "The fllm-iormlng solutions of the preceding Acetone i a Dl m who; 30 Exam les 1-8 are also very suitable used as. ad-

hesives tor sticidn: ordinary cellulose acetate sheet to itself or to other materials, for instance, paper'or cardboard or for sticking-sheets Special cellulose acetate I or the special cellulose acetate to such materials. Acetone The solutions described in ExamplesB-ll are Ethyl alcohoL' I suitable for making tilms and toils of thickness' vWater V 50 rangingvtrom 0.00l"-0.030" or even higher. Dlacetone alcohol 9 Solutions suitable for the formation or films or e coatings by spraying can be obtained by diluting 3mm?" any of the solutions reierred to above with more cellulose mu I g: solvent. The iollowin: is an example or such a mguudne meta (6mm) a 5 diluted solution based on Example 6 above.

Acetamm knample .9 Alcohol as Parts i 5o Cellulose acetate 20 Dmewne w 5 Methylene oitricacid sLvcerol-resin l q i A a water-i- 10o 3mm! 5 Dioxane 100 The following examples illustrate the producg gg g rgfigf y 1-31 11: tion of cellulose ac mes accordinl to'the mwmr, 1 m vention; e i V i 100 35 Emmpl 1 Etlwl' lacta e 15 109 parts of cellulose are pretreated for 12 r u h hours at 30-40 C'. wi th 100 parts of acetic acid. The dummy] ph an be rammed by The mass is then addeki to a mixture, precooled 33" "F 01mm (mum "T 40 to about 10' 0.. or zoo parts of acetic acid. sop 1 1 j m parts of acetic anhydride and 15 parts oi sulphuric acid. Acetylation is allowed to continue m 1; E 1, 1, until all the cellulose has dissolved, the' temex Q1: m 'i ng :ol li tlon l s com- Denture not beinl allowed to rise above about 7 r no of 11mm e n; v g t, 5 C. 40-50 parts .of water are then added and minimum-column; in 40% aqueous acetone. 10 n s f c d .br w n h mixture to re or methylene time acid-glycerol min. stood at I temperature or 4 C- n l a no part; 41 and 50 part when The sample removed is soluble in a aqueous s0- neghylme ig-1 uidqlywol gm 4; m by lutionoracetone. Premature precipitation durnew ittlA of methylene citric acid with w 8 l' a I! avoided by the addition or my a m of 1 5 -51 in in open "58,1 30mg, 4 ther quantities oi water from time to time. will atest sample :eilwhen heated for 10 min- The 11111080 Q S is then prec pi a ed l h at 1; 135,1go", t m m ui m additional acetone, -iiltered, washed in acetone 1.". described'in Britishfat'ent No. scam 111-. mildfledstun! of methylene citric acid and :lycerol;- Emmple ll jcordensation may be in aslmilar way between citri u'glycerol and paraiqrmaldesmith mum mtyhuon' the mpemtum' h d'e.

3 maintained at that temperature until a sasliple the m is carried out as in example 6 so of the mtltels soluble in 0% aqueous acetone. exeepththat the illm-torminksoiutlon contains 39cm F i 111 aeltrlc we [lycerolxesin instead oi the methyl- P10 10. n thlt a m s crter Period 0 ene feitrlc wcid-a'lyoerol resin. "F l i luired to obtain the desired solubilacld-ilyc'erol resin is made by 0011- 2o parts ofcltricaeid sndglidpalgtsfit c5 3mm, cerol'ln'thesamewayas'is esc 1 w ple. 6 for the production of the methylene mo 11mm pletlieaud citric acid-glycerol resin. In place oi glycerol, 700 of dflfl flj a fl 1;!- 31m!" m; W1 .may be employed. drochioric acid at temperature 0 -6 C. or m m, of w w m cm or 3 15 hours according to the proportion of hydro W 1d h proportion; helm, mmtmly chloric acid present. The mixture isthen cooled equjmolecuh'r to about 10' 6.; 300 parts of acetic anbydride are gm 3 f added and acetyiatlon and ripening are carried H out as described in Example 10, except that a.- The process is carried out as in Example 8 7e much shorter period oi ripening will be found necessary to obtain the desired solubility prop erties.

In Examples -12 at least a part of the sulphuric acid used as the acetylation catalyst can be replaced by phosphoric acid In a similar way. other esters of cellulose having the desired solubility properties can be made, for example. cellulose propionate or butyrate.

Having described my invention, what I desire to secure by letters Patent is:

1. An article having a window. and such that when in use said window is liable to be exposed on one side to a moist warm atmosphere and on the other side to a colder atmosphere; said window having a transparent closure comprising a sheet at least one surface of which is composed largely oi. an organic derivative of celluloss which is insoluble in water but soluble in a liquid mixture containing a neutral organic liquid and at least the same amount or water.

2. A respirator face-piece having at least one eye-piece closed by a transparent sheet at least one suriace 01 which is composed largely of an organic derivative of cellulose which is insoluble in water but soluble in a liquid mixture containing a neutral organic liquid and at least the some amount of water.

3. An article having a window, and such that when in use said window is liable to be exposed on one side to a moist warm atmosphere and on the other side to a colder atmosphere, said window having a transparent closure comprising a sheet at least one surface oi which is composed largely of cellulose acetate which is insoluble in water but soluble in a. liquid mixture containing acetone and at least the same amount or water.

4. A respirator face-piece having at least one ey'epiece closed by a transparent closure comprising a sheet having a basis of an organic derivative of cellulose which is insoluble in water but soluble in a liquid'mlxture containing a neutral organic liquid and at least the same amount of water, said sheet being stuck to a sheet of wator-impermeable material and the resulting composite sheet being so positioned that the surface containing the organic derivative of cellulose is a on the inside of the facepiece.

derivative of cellulose which is insoluble in water but soluble in a liquid mixture containing a neutral organic liquid and at least an equal amount of water, said sheet being separated by an air"- space from a sheet 01' waterdmpermeable material and being so positioned that one of its surfaces is on the inside oi the face-piece.

6. A respirator lace-piece having at least one eye-piece closed by a transparent closure which comprises a sheet of material having a basis of an organic ester of cellulose which is insoluble in water but soluble in a liquid mixture containing a neutral organic liquid and at least the same amount of water, said ester of cellulose being in intimate admirrture with a plasticizer having an amnity for water.

'l. A respirator face-piece having at least one eye-piece closed by a transparent closure which comprises a sheet of material having a. basis of an organic ester oi cellulose which is insoluble in water but soluble in a. liquid mixture containing a neutral organic liquid and at least the same amount of water. said ester of cellulose being in intimate admixture with a synthetic resin having an affinity for water.

8. A respirator face-piece having at least one eye-piece closed by a transparent closure which comprises a sheet of material having a basis of an organic ester of cellulose which is insoluble in water but soluble in a liquid mixture containing a neutral organic liquid and at least the same amount of water, said ester of cellulose being in intimate admixture with a plasticizer having an amnity !or water together with a synthetic resin having such an afiinity.

9. A respirator lace-piece having at least one eye-piece closed by a transparent closure which comprises a sheet of material having a basis of cellulose acetate which is insoluble in water but soluble in a liquid mixture containing acetone and at least the same amount of water. said cellulose acetate being in intimate admficture with a plasticizer having an aflinity for water and with a synthetic resin having such an amnlty, said synthetic resin being a condensation product oi an alcohol containing at least two hydroxy groups with a substance selected from the class consisting of hydroxy polycarboxylic acids, tormals oi such acids and fatty acid esters o't' such acids.

WILLIAM HENRY MOSS. 

